1. Field of the Invention
The present invention relates to a guiding mechanism. More specifically, the present invention discloses a guiding mechanism for use in an image capturing device, such as a scanner.
2. Description of the Prior Art
Please refer to FIG. 1 and FIG. 2. FIG. 1 is a diagram of a guiding mechanism 20 for use in an image capturing device 10 according to the prior art. FIG. 2 is an exploded diagram of the guiding mechanism 20 depicted in FIG. 1. As shown in FIG. 1, the image capturing device 10 comprises a housing 11, a scanning module 14 installed inside the housing 11 for scanning documents, and a driving module 17 for driving the scanning module 14. As shown in FIG. 2, the guiding mechanism 20 comprises a guide shaft 22 and two sleeves 24, each sleeve 24 is installed within two corresponding guide rings 16 of the scanning module 14. When the two sleeves 24 are disposed within the two guide rings 16, the guide shaft 22 passes through the two sleeves 24 to serve as a support for one side of the scanning module 14. Additionally, the image capturing device 10 further comprises a linear frame mechanism 18 for supporting the other side of the scanning module 14, which is smoothly disposed against the linear frame mechanism 18. When the driving module 17 drives the scanning module 14, the scanning module 14 moves along the shaft 22, and is supported by the guide shaft 22 and the linear frame mechanism 18.
Please refer to FIG. 3 and FIG. 4. FIG. 3 is a cross-sectional view of the guiding mechanism 20 depicted in FIG. 1 along a line 3—3. FIG. 4 is a force diagram of the scanning module 14 depicted in FIG. 1 when the scanning module 14 is acted upon by an external force. As shown in FIG. 3, a direction along an X-axis (as indicated by the arrow labeled with an “X”) is the direction of gravitational force. Dotted line 26 illustrates a line of gravity along the X-axis that is the center of gravity for the sleeve 24. When the guide shaft 22 passes through the sleeve 24, a gap 28 must be maintained between the guide shaft 22 and the sleeve 24 to permit the scanning module 14 to move along the guide shaft 22, and the spacing of the gap 28 must be kept fairly limited. If the spacing of the gap 28 is too narrow, the driving module 17 must provide a larger driving force to overcome friction between the guide shaft 22 and the sleeve 24. If the spacing of the gap 28 is too great, vibration will occur when the scanning module 14 scans a document. The inner surface 25 of the sleeve 24 is a smoothly curved surface, and so if the spacing of the gap 28 is too wide, the guide shaft 22 and the sleeve 24 will meet at what is effectively a single contact point 29. With gravity pulling the sleeve 24 against the guide shaft 22, the scanning module 14 is easily wobbled by a horizontal force. This is shown in FIG. 4. When the scanning module 14 is under a static condition of the gravitational force mg countered by the supporting force F, the scanning module 14 will suffer wobbling in the horizontal direction if the scanning module 14 experiences an unexpected horizontal force F″. The sleeve 24 must be tightly disposed within the inner surface of the guide ring 16 to prevent the sleeve 24 from slipping out of the guide ring 16. A manufacturer typically designs the external diameter of the sleeve 24 to be larger than the internal diameter of the guide ring 16. A large force must be used to install the sleeve 24 inside the guide ring 16, which is inconvenient for the manufacture when fabricating the sleeve 24, especially, if interference portions when manufacturing the sleeve 24 and the guide ring are generated too much, damage to the sleeve 24 or the guide ring 16 may occur.